Gas Diffusion: HCl & NH3 Reaction Time

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Discussion Overview

The discussion revolves around an experiment involving the diffusion of gases, specifically hydrochloric acid (HCl) and ammonia (NH3), through a glass tube. Participants explore the factors affecting the reaction time between the two gases, including molecular velocities and sizes.

Discussion Character

  • Exploratory, Technical explanation, Conceptual clarification

Main Points Raised

  • One participant notes that the gases took about 5 minutes to meet and react, despite the high mean velocities of the gas molecules at 25 degrees Celsius being around 500 m/s.
  • Another participant suggests that the high velocity of HCl molecules is countered by frequent collisions with other HCl molecules, which slows down the overall movement, likening it to a crowded scenario.
  • A participant questions whether the size of the molecules affects the transit time, proposing that NH3 might be larger and thus complicating the diffusion process.
  • In response, another participant clarifies that HCl molecules are actually larger and that this size difference contributes to their slower movement compared to the lighter NH3 molecules, referencing Graham's law of diffusion.

Areas of Agreement / Disagreement

Participants express differing views on the impact of molecular size on diffusion time and the implications of molecular collisions, indicating that the discussion includes multiple competing perspectives.

Contextual Notes

There are unresolved aspects regarding the specific effects of molecular size and the assumptions underlying the application of Graham's law in this context.

erjkism
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i did an experiment involving gas diffusion through a glass tube. HCl was on one side of the tube, while NH3 was on the other side. it took about 5 minutes for the gases to meet in the middle of the tube and form a precipitate.

but the mean velociries of the HCL and NH3 gas molecules at 25 degrees celsius are around 500 m/s. why did it take so long for the molecules to meet and react?
 
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Most of the time the 500m/s HCL molecule is bouncing off other HCL molecules.
Imagine a crowd where everyone is running around in circles bumbing into each other - the crowd as a whole only moves very slowly.
 
k thanks
 
But would not the size of the molecules also effect the transit time. Not being a wise guy, just trying to learn as well. My thinking is the NH3 would be larger, so it would be like cramming a bunch of stuff in a small hole.
 
actually the HCl molecules are larger, and they ended up going quite a bit slower than the lighter NH3 molecules. It goes along with grahams diffusion rate equations
 

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